L84 Fuelie Motor On Engine Dyno - Fuelie Fisticuffs

The Carbed L76 Takes On The Injected L84 On An Engine Dyno

When was the last time you saw a Rochester fuel-injection system on an engine dyno?

Just a few short years after Chevy introduced the original 265 small-block, the company followed up by offering a true legend in the form of the fuel-injected 283. Often touted as the first mass-produced motor to offer 1 horsepower per cubic inch, the fuelie 283 started a small-block Chevy performance trend that would continue for decades. The 283hp 283 of 1957 was eventually replaced with Chevy's new wonder motor, the 327. Compared with the 283, the 327 offered an increase in both bore (from 3.875 to 4.00 inches) and stroke (from 3.00 to 3.25 inches). Continuing the performance trend started a few years earlier, Chevy topped the hot 327 with the latest version of its mechanical FI setup. The pinnacle of this combination was the famous L84 fuelie motor that offered no fewer than 375 hp in 1964 and 1965.

Whereas the fuelie 283 offered 1 hp/ci, the L84 sported an amazing 1.146 hp per cube. In fact, until the release of the quad-cam LT5 in the ZR1, the L84 was the highest-rated production small-block ever offered by Chevrolet. Of course, there's a major difference between the gross power numbers of the muscle-car era and the modern net-rated versions. Gross ratings were obtained on an engine dyno under ideal conditions and without accessories. The current net ratings comply with SAE standards and are taken at operating temperature, using the factory tune, and with full accessories, induction, and exhaust (including catalytic converters). Thus the 375hp L84 is likely closer to 325 hp by today's more exacting standards.

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Though the L76/L84 engines were originally equipped with two-bolt blocks, our test 327 started out with a four-bolt piece courtesy of L&R Machine. L&R honed and bored it 0.030 over to make way for a new set of forged pistons.

Looking at the specs of the L84, you can see that the 327's power came courtesy of an elevated compression ratio, a set of high-performance heads, and aggressive cam timing. Back in the days of high-test fuel, factory motors could get away with a combination of iron heads and the 11.0:1 compression offered in the L84. Similarly, the L84's hairy solid-lifter cam yielded a crotchety low-speed idle that wouldn't be tolerated in the modern era. Whereas lesser motors offered 1.94/1.50 valves, the "double hump" fuelie heads (461 castings) sported a larger 2.02/1.60 combination. Of course, the main reason anyone purchased the L84 was the Rochester FI system. Interestingly, other than the fuelie induction system, the L84 was the same motor as the carbureted, 365hp L76.

Sales figures indicate that the L76 was much more popular than the L84. There are two distinct reasons for this, the first being price. While the L76 cost just $129 more than the base engine, the fuelie motor tacked on a whopping $538, or $246 more than the 425hp 396! Another factor was that fuel injection was completely foreign to most enthusiasts at the time. In fact, a great many fuelie owners removed the injection setup altogether and replaced it with a single- or dual-quad combo for street/strip racing.

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Sorting through their many available cores, the L&R crew were able to locate a suitable 3.25-inch 327 crank to fit our large-journal block.

The popularity of the carbureted engine and the general inaccuracy of the output ratings of the time gave rise to an interesting question: What was the real difference in power between these legendary small-blocks? Did the L84 really produce 10 more peak horses than its carbureted sibling? If so, what was the difference in power elsewhere along the curve? And what about fuel metering? Did the injected combination improve the air/fuel curve compared with carburetion?

The HardwareTo accurately answer these questions, we needed to first build a suitable test motor. We decided to assemble not just a small-block, but something that would replicate the original 327 combinations of 1965. This meant an 11.0:1 327 equipped with period-correct cylinder heads, a reproduction of the original solid-lifter cam, and the factory high-rise intake. Obviously we also had to have an original Rochester FI system on hand to compare to the carbureted combo.

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L84 Fuelie Motor On Engine Dyno - Fuelie Fisticuffs

When was the last time you saw a Rochester fuel-injection system on an engine dyno?

Though the L76/L84 engines were originally equipped with two-bolt blocks, our test 327 started out with a four-bolt piece courtesy of L&R Machine. L&R honed and bored it 0.030 over to make way for a new set of forged pistons.

Sorting through their many available cores, the L&R crew were able to locate a suitable 3.25-inch 327 crank to fit our large-journal block.

To achieve the desired 11.0:1 compression, the forged pistons (right) required a slight dome. This photo shows one next to a smaller-domed 350 piece.

Elgin Industries supplied the reproduction Duntov 30-30 cam. In addition to cams and other engine components, Elgin carries a great many factory suspension components for early muscle cars.

The necessary gasket set, oil pump, and neutral damper all came from Pro Comp.

Pro Comp also supplied a new set of stainless steel valves, while Comp Cams came through with the necessary valvesprings and retainers. These springs provided 125 pounds of seat pressure, which allowed our 327 to rev safely to 7,000 rpm.

Fuelie heads typically feature 64cc combustion chambers, though ours were slightly smaller at 62.5 cc. They had obviously been milled a few times in their long life.

The heads received a number of valvetrain components from Comp, including factory long-slot rockers, guide plates, and rocker studs.

L&R freshened up the stock heads with a light surface and a factory-style valve job. The reconditioned heads flowed 205 cfm on the intake and 140 cfm on the exhaust.

Topping off the fuelie heads was an original high-rise intake wearing a 461 casting number. This dual-plane unit came courtesy of Rick Stoner from Westech.

Unfortunately, the original intake had previously been modified to eliminate its center divider. We cured this problem by fabricating a replacement divider out of sheet aluminum. Back-to-back tests on both configurations found a significant torque loss (7-8 lb-ft) without the divider, along with a minor power gain (2-3 hp) at the top of the rev range.

Rather than run a factory Holley 3310, we opted for a modern version in the form of a 750 Street HP. With the proper jetting, the two carbs would perform equally well on our 327.

If you must have a numbers-matching carburetor on your L76, check with the guys at Pony Carburetors. They have a wide variety of original, restored carbs for muscle-car and Corvette applications.

Rather than run the engines with the factory cast-iron exhaust manifolds, we chose a set of long-tube dyno headers. Note that we also ran them sans accessories with a Meziere electric water pump.

On the dyno, the carbureted L76 produced peak numbers of 355 hp and 366 lb-ft of torque.

Next up was the factory fuel injection. This system came courtesy of fuelie legend Chuck Smith and retired Delta Airlines captain Mark Detwiler.

After removing the carbureted intake, we installed the lower manifold using a fresh set of Fel-Pro 1205 intake gaskets.

Next came the upper injection manifold and assembly. The pre-assembled fuelie assembly could be installed as one unit.

Whereas the carbureted motor was run with an MSD billet distributor, the Rochester fuel-injection required a dedicated distributor. In addition to a mechanical tach drive, the fuelie distributor also featured a drive output for the mechanical fuel pump.

To achieve the desired air/fuel ratio on our injected 327, it was necessary to increase the size of the fuel injectors. Smith installed a set of "Z" nozzles (the largest available), which worked perfectly.

On the dyno, the fuelie Vette motor showed its worth by out-powering the carbureted combination to the tune of 9 hp. Peak numbers checked in at 364 horses and 363 lb-ft of torque. Note that peak torque occurred at a higher engine speed with the fuel injection than with the carburetor.

Before pulling the 327 off the dyno, we decided to run a cam-comparison test. We replaced the Elgin reproduction stick with a modern solid flat-tappet unit from Comp Cams. Though down by as much as 18 degrees of duration, the Comp grind increased peak power from 355 to 370 hp. Peak torque was up as well, from 366 to 380 lb-ft.

Graph 1: L76 vs. L84The dual-plane 461 intake and Holley carb offered slightly better torque from 3,300 rpm to 4,300 rpm, but the fuelie setup pulled away thereafter. Credit the unique tunnel-ram intake design of the fuel-injected motor, along with its near-ideal air/fuel curve. While the Rochester fuel injection has a reputation of being finicky, it's actually not much more difficult to tune than a conventional carburetor.

Graph 2: Duntov 30-30 Repro Cam vs. Comp XS274HReplacing the Duntov 30-30 reproduction cam with the XS274H from Comp improved the power output of the 327 between 3,000 and 7,000 rpm. The peak numbers, meanwhile, improved from 355 hp and 366 lb-ft to 370 hp and 380 lb-ft. The gains were as great as 20 hp and a like amount of torque at other points along the curve.

Check out this High Performance Chevy Engine with a Comp valvetrain, a Dart induction, a Carb Shop carburetor and a F2 Procharger, Featured in the 2007 December Issue of Chevy High Performance Magazine. » Read More